Recording media having protective overcoats of highly tetrahedral amorphous carbon and methods for their production

ABSTRACT

The invention provides systems and methods for the deposition of an improved diamond-like carbon material, particularly for the production of magnetic recording media. The diamond-like carbon material of the present invention is highly tetrahedral, that is, it features a large number of the sp 3  carbon-carbon bonds which are found within a diamond crystal lattice. The material is also amorphous, providing a combination of short-range order with long-range disorder, and can be deposited as films which are ultrasmooth and continuous at thicknesses substantially lower than known amorphous carbon coating materials. The carbon protective coatings of the present invention will often be hydrogenated. In a preferred method for depositing of these materials, capacitive coupling forms a highly uniform, selectively energized stream of ions from a dense, inductively ionized plasma. Such inductive ionization is enhanced by a relatively slow moving (or “quasi-static”) magnetic field, which promotes resonant ionization and ion beam homogenization.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of and claims the benefit of priorityfrom U.S. patent application Ser. No. 10/354,336, filed Jan. 29, 2003,now U.S. Pat. No. 6,740,384, which is a divisional of and claims thebenefit of priority from U.S. patent application Ser. No. 09/648,341,filed Aug. 25, 2000, now U.S. Pat. No. 6,544,627, which is acontinuation of U.S. patent application Ser. No. 09/165,513, filed Oct.2, 1998, now U.S. Pat. No. 6,537,668, which is a divisional of U.S.patent application Ser. No. 08/761,336, now U.S. Pat. No. 5,858,477,filed Dec. 10, 1996, which is a continuation-in-part of and claimspriority from U.S. Provisional Patent Applications Ser. No. 60/018,793,filed May 31, 1996, and Ser. No. 60/018,746, filed May 31, 1996, thefull disclosures of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to thin films and methods fortheir deposition, and more particularly, provides diamond-like films,plasma beam deposition systems, and methods useful for production ofdiamond-like protective overcoats on magnetic recording media and otherindustrial applications.

In recent years, there has been considerable interest in the depositionof a group of materials referred to as diamond-like carbon. Diamond-likecarbon can generally be defined as a metastable, high density form ofamorphous carbon. Diamond-like carbon is valued for its high mechanicalhardness, low friction, optical transparency, and chemical inertness.

Deposition of diamond-like carbon films often involves chemical vapordeposition techniques, the deposition processes often being plasmaenhanced. Known diamond-like films often include carbon with hydrogen,fluorine, or some other agent. The durability and advantageouselectrical properties of diamond-like carbon films have led to numerousproposals to apply these films to semiconductors, optics, and a widevariety of other industrial uses. Unfortunately, the cost and complexityof providing these advantageous diamond-like carbon films using knownchemical vapor deposition processes has somewhat limited their use.Furthermore, while a wide variety of diamond-like carbon coating filmshave been deposited in laboratories, many of these films have been foundto have less than ideal material characteristics.

A very different form of amorphous carbon is generally applied as aprotective overcoat for magnetic recording media. Magnetic recordingdisks generally comprise a substrate having a magnetic layer and anumber of underlayers and overlayers deposited thereon. The nature andcomposition of each layer is selected to provide the desired magneticrecording characteristics, as is generally recognized in the industry.

The information stored in magnetic recording media generally comprisesvariations in the magnetic field of a thin film of ferromagneticmaterial, such as a magnetic oxide or magnetic alloy. Usually, aprotective layer is formed over the top of the magnetic layer, and alayer of lubricating material is deposited over the protective layer.These protective and lubricating layers combine to increase thereliability and durability of the magnetic recording media by limitingfriction and erosion of the magnetic recording layer. Sputteredamorphous carbon films have gained widespread usage as protectiveovercoats for rigid magnetic recording disks.

Sputtered amorphous carbon overcoats have been shown to provide a highdegree of wear protection with a relatively thin protective layer.Magnetic recording disk structures including sputtered amorphous carbonhave been very successful and allow for quite high recording densities.As with all successes, however, it is presently desired to providemagnetic recording disks having even higher recording densities.

Recording densities can generally be improved by reducing the spacingbetween the recording transducer, called the read/write head, and themagnetic layer of the magnetic recording disk (or more specifically,between the read/write head and the middle of the magnetic layer). Inmodern magnetic recording systems, the read/write head often glides overthe recording surface on an air bearing, a layer of air which moves withthe rotating disk. To minimize frictional contact between the rotatingdisk and the read/write head, the disks surface is generally rougher(and the glide height therefore higher) than would otherwise be idealfor high density magnetic recording. Even if this glide height isreduced (or eliminated), the read/write head will be separated from therecording layer by the protective amorphous carbon overcoat. Thisprotective layer alone may, to provide the desired media life, limit theareal density of the media. Generally, overcoat layer thicknesses aredictated by durability and continuity limitations. Sputtered carbonfrequently becomes discontinuous at thicknesses below about 50 Å. Thus,the durability requirements of rigid magnetic recording media generallydictate that the distance between the read/write head and the magneticrecording layer be maintained, even though this limits the areal densityof the magnetic recording media.

It has previously been proposed to utilize known chemical vapordeposition techniques to deposit a variety of diamond-like carbonmaterials for use as protective coatings for flexible magnetic recordingtapes and magnetic recording heads. Unfortunately, known methods forchemical vapor deposition of diamond-like materials, including plasmaenhanced methods, generally subject the substrate to temperatures ofover 500° C., which is deleterious for most magnetic disk substrates.Therefore, these known diamond-like carbon films do provide relativelygood hardness and frictional properties, they have found littlepractical application within the field of rigid magnetic recordingmedia, in which sputtered amorphous carbon protective overcoats areoverwhelmingly dominant.

For these reasons, it would be beneficial to provide improved magneticprotective overcoats with improved read/write head frictional and glidecharacteristics (generally called stiction) for recording media.Preferably, such an improved overcoat will provide durability andreliability without having to resort to the density-limiting glideheights and/or protective overcoat thickness of known rigid magneticrecording media, and without subjecting the media substrates toexcessive temperatures.

It would also be desirable to provide improved diamond-like carbonmaterials and methods for their deposition. It would be particularlydesirable if such materials and methods could be utilized for practicalrigid magnetic recording media with reduced spacing between theread/write head and the magnetic recording layer, ideally by providing aflatter, smoother, and thinner protective coating which maintained oreven enhanced the durability of the total recording media structure. Itwould also be advantageous to provide alternative methods and systemsfor depositing such protective layers, for use in the production ofmagnetic recording media, as well as integrated circuits, optics,machine tools, and a wide variety of additional industrial applications.

2. Description of the Background Art

U.S. Pat. No. 5,182,132 describes magnetic recording media having adiamond-like carbon film deposited with alternating circuit plasmaenhanced chemical vapor deposition methods. U.S. Pat. No. 5,462,784describes a fluorinated diamond-like carbon protective coating formagnetic recording media devices. European Patent Application 700,033describes a side-mounted thin film magnetic head having a protectivelayer of diamond-like carbon. European Patent Application No. 595,564describes a magnetic recording media having a diamond-like protectivefilm which consists of carbon and hydrogen.

U.S. Pat. No. 5,156,703 describes a method for the surface treatment ofsemiconductors by particle bombardment, the method making use of acapacitively coupled extraction grid to produce an electrically neutralstream of plasma. V. S. Veerasamy et al. described the properties oftetrahedral amorphous carbon deposited with a filtered cathodic vacuumarc in Solid-State Electronics, vol. 37, pp. 319-326 (1994). The recentprogress in filtered vacuum arc deposition was reviewed by R. L. Boxmanin a paper presented at the International Conference of MetallurgicalCoatings and Thin Films located at San Diego in April of 1996. Electroncyclotron wave resonances in low pressure plasmas with a superimposedstatic magnetic field were described by Professor Oechsner in PlasmaPhysics, vol. 15, pp. 835-844 (1974).

SUMMARY OF THE INVENTION

The present invention provides systems and methods for the deposition ofan improved diamond-like carbon material, particularly for theproduction of magnetic recording media. The diamond-like carbon materialof the present invention is highly tetrahedral, that is, it features alarge number of the Sp³ carbon-carbon bonds which are found within adiamond crystal lattice. The material is also amorphous, providing acombination of short-range order with long-range disorder, and can bedeposited as films which are ultrasmooth and continuous (pin-hole free)at thicknesses substantially lower than known amorphous carbon coatingmaterials. The carbon protective coatings of the present invention willoften be hydrogenated, generally providing a significantly higherpercentage of carbon-carbon sp³ bonds than known hydrogenated amorphousdiamond-like carbon coatings having similar compositions, and mayoptionally be nitrogenated. In a preferred method for depositing ofthese materials, capacitive coupling forms a highly uniform, selectivelyenergized stream of ions from a dense, inductively ionized plasma. Suchinductive ionization is enhanced by a relatively slow moving (or“quasi-static”) magnetic field, which promotes resonant ionization andion beam homogenization. Clearly, the materials, systems, and methods ofthe present invention will find applications not only in the field ofmagnetic recording media and related devices, but also in integratedcircuit fabrication, optics, machine tool coatings, and a wide varietyof film deposition and etching applications.

In a first aspect, the present invention provides a method for producingmagnetic recording media, the method comprising forming a magnetic layerover a substrate, and ionizing a source material so as to form a plasmacontaining carbon ions. The carbon ions are energized to form a streamfrom the plasma toward the substrate, so that carbon from the ions isdeposited on the substrate. The ions impact with an energy whichpromotes formation of sp3 carbon-carbon bonds. Advantageously, such amethod can form a highly tetrahedral amorphous carbon protective layer,generally having more than about 15% sp³ carbon-carbon bonds. Generally,the impact energy of the energetic carbon ions is within apre-determined range to promote formation of the desired latticestructure, the bonds apparently being formed at least in part bysubplantation. Preferably, each carbon ion impacts with an energy ofbetween about 100 and 120 eV. In many embodiments, the resulting highlytetrahedral amorphous carbon protective layer includes more than about35% sp³ carbon-carbon bonds, with particularly preferred methodsproducing more than about 70% sp³ carbon-carbon bonds.

Generally, the stream will be primarily composed of ions having auniform weight, and the impact energy will preferably be substantiallyuniform. In some embodiments, this uniformity is promoted throughfiltering of the ion stream. In such cases, the energizing stepgenerally comprises striking a plasma using a solid cathodic arc ofcarbon source material. Alternatively, the stream will be energized byapplying an alternating potential between a coupling electrode and anextraction grid so as to self-bias the plasma relative to the extractiongrid through capacitive coupling, thereby extracting the ion streamthrough the grid. Hydrogen and/or nitrogen may also be included, both inthe ion stream and the protective layer.

In another aspect, the present invention provides magnetic recordingmedia comprising a substrate, a magnetic layer disposed over thesubstrate, and a protective layer disposed over the magnetic layer. Theprotective layer comprises a highly tetrahedral amorphous carbon,generally having more than about 15% sp³ carbon-carbon bonds.Preferably, these bonds are formed at least in part by directing anenergetic stream of carbon ions onto the substrate. In many embodiments,the protective layer includes more than about 35% sp³ carbon-carbonbonds, with particularly preferred embodiments including more than about70% sp³ carbon-carbon bonds. Such protective layers are ultrasmooth andcontinuous at thicknesses of less than about 75 Å, and will providedurable recording media even at thicknesses of less than about 50 Å.Furthermore, the hardness and tribological performance of these denseprotective materials may allow highly durable recording media with arealrecording densities of over 1 gigabyte per square inch with reducedread/write head glide heights of lower than about 1 μ″, optionallywithin a near-contact or continuous contact recording systems.

In another aspect, the present invention provides a method for enhancingan ion beam, the ion beam produced by confining a plasma within a plasmavolume, inductively ionizing the plasma, and forming a stream of ionsfrom within the plasma volume by capacitive coupling. The methodcomprises moving a magnetic field through the plasma to promote resonantinductive ionization, preferably by sequentially energizing each of aplurality of coils disposed radially about the plasma volume.

In another aspect, the present invention provides an inductiveionization system for use with an ion-beam source. The source includesan antenna disposed about a plasma volume for inductively ionizing aplasma therein. A coupling electrode is exposed to the plasma volume andan extraction electrode is disposed over an opening of the plasmavolume, so that the extraction electrode is capable of expelling ions ofthe plasma through the grid by capacitive coupling. The system comprisesat least one coil disposed adjacent the plasma volume capable ofapplying a transverse magnetic field to the plasma volume so as topromote resonant inductive ionization by the antenna. The magnetic fieldcan be moved through the plasma container to homogenize the expelled ionstream. This movement of the magnetic field, which is optionallyprovided by selectively energizing coils radially disposed about theplasma volume, may also further densify the plasma by promoting particlecollisions through a churning or mixing effect.

In another aspect, the present invention provides a diamond-likematerial comprising carbon in the range between about 72 and 92 atomicpercent, and hydrogen in the range between about 8 and 18 atomicpercent. The material is amorphous, and between about 15 and 85 percentof carbon-carbon bonds are sp³ bonds. Generally, sp³ bond formation willbe promoted with subplantation using ion-beam deposition from a plasmabeam source, so that the number of such bonds will be higher than knownmaterials having similar compositions. Hence, the highly tetrahedralamorphous carbon and hydrogenated carbon of the present invention willhave fewer polymer-like hydrogen chains, and will generally exhibitenhanced thermal and mechanical stability.

In another aspect, the present invention provides a method fordeposition of highly tetrahedral amorphous carbon over a substrate, themethod comprising ionizing a source material to form a plasma andconfining the plasma within a plasma volume. The plasma is capacitivelycoupled to form a stream flowing outwardly from within the plasmavolume. The stream includes carbon ions from the plasma and is directedonto the substrate. Advantageously, such a method allows deposition ofcarbon ions of uniform size with a uniform energy, and allows tailoringof the energetic carbon ions to specifically promote sp³ bonding throughsubplantation. The source material typically comprises a gas having asubstantially coherent dissociation energy spectra, the source gasideally comprising acetylene. Preferably, the ions strike the substratewith an impact energy of between about 57 and 130 eV for each carbonatom, ideally being between about 80 and 120 eV each.

In another aspect, the present invention provides an ion-beam sourcecomprising a container defining a plasma confinement volume. Thecontainer has an opening, and an antenna is disposed about the plasmavolume so that application of a first alternating potential to theantenna is capable of inductively ionizing a plasma therein. A couplingelectrode is electrically coupled to the plasma volume and an extractionelectrode is disposed over the opening of the container. The extractionelectrode has a surface area which is substantially less than thecoupling electrode surface, so that application of a second alternatingpotential between the coupling electrode and the extraction electrode iscapable of expelling ions of the plasma through the grid. Preferably, atleast one coil is disposed adjacent the container, and is capable ofapplying a transverse magnetic field to the plasma volume, therebypromoting highly efficient inductive ionization resonance by theantenna. Ideally, the magnetic field can be moved through the plasmacontainer to homogenize the expelled ion stream. This movement of themagnetic field, which is optionally provided by selectively energizingcoils radially disposed about the plasma confinement volume, may furtherdensity the plasma by promoting particle collisions with a churning ormixing effect.

In yet another aspect, the present invention provides an ion-beam sourcecomprising plasma containment means for confining a plasma within aplasma volume. Inductive ionization means inductively couples a firstalternating current with the plasma so as to ionize the plasma withinthe plasma volume. A moving magnetic field generation means providesresonant densification and homogenization of the ionized plasma withinthe plasma volume. Ion extraction means forms a stream of ions out fromthe plasma volume.

In another aspect, the present invention provides a method for producingan ion beam, the method comprising confining a plasma within a plasmavolume, inductively ionizing the plasma, and forming a stream of ionsfrom within the plasma volume by capacitively coupling the plasma withan extraction grid. This capacitive coupling self-biases the plasmarelative to the grid, and can be used to produce a quasi-neutral plasmastream. Generally, a transverse magnetic field is applied to density theplasma by promoting resonant inductive ionization. Ideally, the magneticfield is moved through the plasma volume to homogenize the plasma andplasma stream.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a magnetic recording disk includingthe tetrahedral amorphous hydrogenated carbon protective layer of thepresent invention.

FIGS. 1A and B illustrate the effects of nitrogen doping on thetetrahedral amorphous hydrogenated carbon of the present invention.

FIGS. 2 schematically illustrates a method for depositing the highlytetrahedral amorphous hydrogenated carbon over the disk of FIG. 1, andalso shows a hybrid inductive/capacitive plasma beam source according tothe principles of the present invention.

FIG. 2A is a cross-sectional view of the hybrid source of FIG. 2,showing the inductive ionization antenna and quasi-static magnetic fieldgenerating coils which density and homogenize the plasma.

FIG. 3A illustrates an alternative method and system for depositinghighly tetrahedral amorphous hydrogenated carbon over the disk of FIG. 1using an acetylene plasma from a plasma beam source.

FIGS. 3B and C illustrate capacitive coupling of the plasma to extract astream of ions when using the plasma beam source of FIG. 3A.

FIG. 3D illustrates an alternative embodiment of a plasma beam source,in which the effective area of the coupling electrode can be varied toprovide further control over the ion density and ion energy.

FIGS. 3E and F illustrate operating characteristics of plasma beamsources for deposition of diamond-like carbon.

FIGS. 4A and B illustrate known resonant inductive ionization of aplasma with a fixed magnetic field.

FIGS. 4C and D explain densification of the plasma provided by ElectronCyclotron Wave Resonance.

FIG. 5 illustrates an alternative method and deposition system forproducing the recording disk of FIG. 1, which system relies upon afiltered cathodic arc for deposition of the highly tetrahedral amorphoushydrogenated carbon material of the present invention.

FIGS. 6A-8 show experimental data, as described in detail in theexperimental section.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

Referring now to FIG. 1, a rigid magnetic recording disk 2 comprises anon-magnetic disk substrate 10, typically composed of an aluminum alloy,glass, ceramic, a glass-ceramic composite, carbon, carbon-ceramiccomposite, or the like. An amorphous nickel-phosphorus (Ni—P) layer 12is formed over each surface of the disk substrate 10, typically byplating. The Ni—P layer is hard, and imparts rigidity to the aluminumalloy substrate. A chromium ground layer 14 is formed over Ni—P layer12, typically by sputtering, and a magnetic layer 16 is formed over theground layer 14. Please note that these layers are shown schematicallyonly, as NiP layer 12 will typically be much thicker than the otherlayers.

The magnetic layer 16 comprises a thin film of a ferromagnetic material,such as a magnetic oxide or magnetic alloy. Magnetic layer 16 istypically sputtered over ground layer 14 in a conventional manner. Themagnetic layer will often be composed of a cobalt alloy, such as aCoCrTaPtB, CoCrPtB, CoCrTa, CoPtCr, CoNiCr, CoCrTaXY (X and Y beingselected from Pt, Ni, W, B, or other elements) or the like. The magneticlayer may be formed as a single layer, or may comprise two or morelayers formed over one another. The thickness of magnetic layer 16 istypically in the range from about 200 Å to 800 Å.

Of particular importance to the present invention is a protective layer18 which is formed over the magnetic layer. The protective layer 18 ofthe present invention will generally comprise a highly tetrahedralamorphous carbon, typically having more than about 15% sp³ carbon-carbonbonds, preferably being more than about 35% sp³ carbon-carbon bonds, andideally being over about 70% sp³ carbon-carbon bonds, as measured usingRaman fingerprinting and electron energy loss spectroscopy. Along withcarbon, protective layer 18 may also include hydrogen, generally formingin the range between about 2 and 30 atomic percent of the protectivematerial, preferably being between 8 and 18 atomic percent. Aconventional lubricating layer 20 is disposed over the protective layer.

Although hydrogen is known to increase the percentage of sp³ bonding ofdiamond-like carbon produced by known chemical vapor depositionprocesses, protective layer 18 will generally include significantly lesshydrogen than comparable known diamond-like films. This compositionaldifference may be explained in part by the formation of sp³ bondsthrough subplantation of the energetic carbon ions during deposition.Effectively, the energetic ions deposited using the methods describedhereinbelow impact on the growing film surface, and are driven into thefilm so as to cause densification. This process may also explain why theprotective layer of the present invention includes a higher percentageof quaternary carbon sites (sp³ carbon sites with no hydrogen neighbors)and greater hardness than known alternative amorphous carbon materials.

The microstructure of conventional hydrogenated amorphous carbonsincludes polymer-like hydrocarbon chains. Although hydrogen enhances theformation of tetrahedrally bonded carbon atoms, above a certainthreshold value of hydrogen content, carbon films become polymeric andhence lose their protective properties. Through subplantation, thematerials of the present invention overcome this limitation. Assubplantation promotes formation of sp³ bonds without relying onadditional hydrogen content alone, polymerization can be avoided. Thisrepresents a substantial advantage over known, more highly hydrogenateddiamond-like carbon materials, in which polymerization significantlylimits both thermal and mechanical stability. In contrast, thecarbon-carbon sp³ bonds of the materials of the present invention willgenerally be stable up to temperatures of about 700° C., so that anenhanced percentage of sp³ bonds with a low hydrogen content representsa significant advantage.

Optionally, the films of the present invention may also be nitrogenated.In contrast to known hydrogenated carbon, the electrical conductivity ofthe present highly tetrahedral amorphous carbon can be controllablyvaried over a wide range by the selective incorporation of nitrogenduring the C₂H₂ plasma beam deposition process described hereinbelow.Advantageously, this variation will be provided without significantlyvarying the structural properties of the film. With conventionalhydrogenated carbon, nitrogen incorporation may be related to theformation of sp² bonds. This will be evident by variations in themechanical and optical properties of the films deposited, for whichharness and optical gap will decrease with nitrogen content. With thepresent film materials and deposition methods, a classic doping effectis observed, in which electrical conductivity can be controllably variedby as much as 5 orders of magnitude or more, as is shown in FIGS. 1A andB. Doping can be provided by varying nitrogen pressure within a plasmavolume of an acetylene fed plasma beam source, typically to providefilms having from about 4 to about 30 atomic percent nitrogen. Thisdoping effect of highly tetrahedral amorphous carbon and hydrogenatedcarbon will find particular application for the fabrication ofintegrated circuits and the like.

The highly tetrahedral amorphous carbon materials of the presentinvention also provide a number of advantages over known protectivelayers for recording media. The bond structure of this material providesphysical properties approaching those of diamond, including a hardnessof over about 50 GPa, with certain species having hardness of up toabout 80 GPa. Furthermore, the present protective overcoats have highdensity, generally being over about 2.5 grams per cubic centimeter, andare also very chemically inert.

Of particular importance to recording media, these coatings are smoothand continuous (pinhole-free) at very low thicknesses, and provide adurable protective layer when deposited to a thickness of less than 75Å, preferably being less than 50 Å thick. In fact, films of over 150 Åmay be more susceptible to delamination, and surface roughness mayincrease with thickness. The high mechanical hardness and low frictionsurfaces provided by these materials lead to enhanced tribologicalperformance, providing recording media which are highly tolerant to themechanical abrasion and contact start-stop demands of modern recordingmedia systems, and allowing increased areal density through reducedseparation between the read/write and the magnetic layer. Thisseparation may be reduced by either a reduction in the protective layerthickness, or by a reduction in head glide height, and preferably by areduction in both. Protective layer 18 is generally in the range betweenabout 30 Å and 70 Å, which will allow the disk to meet recording mediaindustry durability and stiction test requirements.

The composition and characterization of the protective film of thepresent invention are highly dependent on the deposition method, and inparticular, depend strongly on the energy and uniformity of carbon ionsstriking the deposition surface.

An exemplary system and method for depositing protective layer 18 onrigid recording disk 2 will be described with reference to FIGS. 2 and2A. Hybrid ion beam source 30 generally includes an inductive ionizationsystem 32, a quasi-static magnetic field system 34, and a capacitive ionbeam extraction system 36.

In general terms, induction system 32 ionizes a plasma 38. The energytransfer between induction system 32 and plasma 38 is greatly enhancedand homogenized by a transverse magnetic field generated by quasi-staticfield system 34. The deposition ions of plasma 38 are actually directedto recording disk 2 (or to any other substrate on which deposition isdesired, or from which etching will be performed) using capacitivecoupling system 36.

Although hybrid source 30 provides a particularly advantageous systemfor deposition of the protective coating 18, a variety of alternativedeposition systems may also be used. As a plasma beam source depositionsystem shares a number of the features of hybrid source 30, but issimpler in operation, diamond-like carbon deposition using a plasma beamsource 50 will be described with reference to FIGS. 3A-F, after whichother aspects of hybrid source 30 will be explained in more detail.

Referring now to FIG. 3A, the use of plasma beam source 50 for thedeposition of carbon will generally be described with reference todepositing protective layer 18 on magnetic recording media 2. As hasbeen mentioned above, these carbon deposition systems and methods willhave a wide variety of alternative uses, particularly in the areas ofintegrated circuits fabrication, optics, and machine tools.

Plasma beam source 50 includes a plasma container 52 which defines aplasma volume 54 therein. Container 52 is typically an 8 cm diameterglass tube, or may alternatively comprise quartz or the like. A couplingelectrode 56 having a relatively large surface 58 here forms one end ofthe container. Alternatively, the coupling electrode may be disposedwithin or external to the container, and may optionally extend axiallyalong the walls of the container. Regardless, coupling electrode 56 isgenerally electrically coupled to the plasma, to a matching network 60,and to a radiofrequency coupling power supply 62. Plasma coupling system36 includes coupling electrode 56, the frequency generator and matchingnetwork 60, 62, and an extraction grid 64. Typically, the extractiongrid will be grounded as shown.

As is explained more fully in U.S. Pat. No. 5,156,703, the fulldisclosure of which is herein incorporated by reference, extraction grid64 has a much smaller surface area exposed to the plasma than thecoupling electrode 56. In operation, RF power, typically at about 13.56MHz, is supplied by the frequency generator through the matching networkand a capacitor to the coupling electrode. This frequency will often beset by government regulations, and may alternatively be about 27.12 MHz,or some other multiple thereof. The extraction grid typically comprisesa graphite rim 66 defining an aperture, and tungsten filaments which aremaintained under tension. Hence, extraction grid 64 resists anydistortion due to thermal expansion. A number of alternative materialsmay be used in the filaments, the filament materials preferably having alow sputtering yield.

Generally, internal pressure within plasma volume 54 is reduced byremoving gas through vacuum port 68. While the vacuum port is here shownbehind the grid, it will preferably be disposed between grid 64 and disk2. Advantageously, when a plasma is struck between the couplingelectrode and the extraction grid, the plasma shifts to a positive DCpotential with respect to the extraction grid, due to the relativemobility of the electrons as compared to the ions within the plasma.Specifically, the greater mobility of electrons than ions in the plasmacauses the plasma to form a sheath between itself and each electrode.The sheaths act as diodes, so that the plasma acquires a positive DCbias with respect to each electrode.

The total radiofrequency potential V₀ will be divided between thesheaths adjacent the powered electrode and the grounded electrode,according to their respective capacitances. As the extraction electrodeis grounded, the voltage of the plasma itself is given by the EquationV=V ₀(C _(e)/(C _(g) +C _(e)))wherein C_(e) is the capacitance of the coupling electrode, while C_(g)is the capacitance of the extraction grid.

Where the extraction electrode is grounded, this plasma voltage biasesthe plasma relative to the grid, accelerating the ions through theextraction grid and toward the substrate. As can be determined from theabove equation, the plasma beam source allows the biasing voltage to beselectively controlled, providing a highly advantageous mechanism forcontrolling ion impact energy.

As capacitance varies inversely with area, the size of the bias voltageat each electrode can be controlled by varying the electrode areas. Asthe extraction grid has a much smaller area than the coupling electrode,the biasing of the plasma relative to the coupling electrode isrelatively low, so that source 50 provides a fairly efficient use of thesource gas material, which is generally provided through source inlet 70adjacent coupling electrode 56. While some material will be deposited onthe container walls at higher power settings, use of the plasma beamsource in an etching mode may allow self cleaning.

The relationship of electron current, ion current, and theradiofrequency potential is illustrated in FIG. 3B. A simplifiedelectrical diagram for analysis of the plasma, the extraction gridsheath, and the coupling grid sheath, is shown in FIG. 3C.

A still further aspect of the plasma beam source carbon depositionsystem and method of the present invention is illustrated in FIG. 3D.Plasma 74 is here contained within a hyperbolic magnetic field producedby magnets 78. An axially movable coupling electrode 80 is supported bya movable ceramic pipe 82 which slides axially through a ceramic end 84of the plasma container vessel.

The magnetic confinement of the plasma allows the effective area ofcoupling electrode 80 to be varied by moving the coupling electrodeaxially relative to the plasma. This allows the bias voltage (and hencethe ion energy) to be varied without changing the radiofrequency poweror the gas pressure. Alternatively, the ion saturation current density(deposition rate) and ion energy can be varied by changing theradiofrequency power and gas feed stock flow rate. The ion current andion energy distribution can be measured with a Faraday cup 86 in thesubstrate plane 88. FIG. 3E shows variations of ion current and mean ionenergy with electrode position D for a range of radiofrequency powers.

The ion energy depends on at least two factors: the accelerationpotential across the grid sheath, and the energy lost by collisionswithin the sheath. The effects of these factors are illustrated in FIG.3F.

The inset to FIG. 3F shows that the ion energy distribution of theplasma beam is quite sharp, with a width of approximately 5% about thebias voltage. The sharpness apparently arises for at least two reasons.First, ions lose little energy in the low plasma pressure throughcollisions within the sheath. Second, the sheath width varies inverselywith the square root of pressure, so that the sheath is quite wide atlow pressures. Where the ion transit time across the sheath is longerthan the radiofrequency period, the ions may be accelerated by the meanvoltage rather than the instantaneous voltage. The ion energydistribution width is also found to vary linearly with pressure, whichindicates that the ion energy distribution width is controlled mainly byion collisions in and above the sheath.

The decomposition or dissociation of hydrocarbons in plasma 74 dependsstrongly on the source gas, the operation pressure, and the gas flowrate. Usually, hydrocarbon plasmas exhibit a wide spectrum ofhydrocarbon radicals in an ionized and/or neutral state. The plasmacomposition depends on the various chemical pathways in the plasma, andthese depend on the plasma parameters such as electron temperature,electron density, and degree of ionization. As a result, a number ofdifferent ions may be present in the plasma, and the composition maychange markedly under different conditions, making uniform deposition ofhomogeneous hydrogenated carbon materials fairly problematic.

Work in connection with the present invention has shown that acetyleneprovides a highly advantageous source gas because of its relativelysimple dissociation pattern. The plasma decomposition of a molecule canbe described in terms of electron-molecule (primary) and ion-molecule(secondary) collisions, and their associated rate coefficients or theirrelated appearance potentials. Advantageously, the dissociation ofacetylene is dominated by its ionization at an appearance potential of11.2 eV. Acetylene may be unique among the hydrocarbons in having such awell-defined reaction path.

The ionic composition of a plasma beam produced using an acetylenesource gas produces a mass spectra at various plasma pressures which aredominated by the C₂H₂ ⁺ ion and other hydrocarbon ions having two carbonatoms, collectively referred to as the C₂ species. The next mostsignificant ions are the C₄ ions, which have been found to decrease inintensity as the pressure is lowered, being below 5% if the pressure ismaintained below 5×10⁻⁵ mbar. For these reasons, carbon deposition usingthe plasma beam source and hybrid source of the present invention ispreferably performed using a feed stock which comprises acetylene.Optionally, N₂, NF₃, or some other nitrogen feedstock may also beincluded to provide nitrogenated films.

The particle flux or stream provided by a plasma beam deposition systemor a hybrid deposition system will generally have a higher degree ofionization than conventional deposition techniques. The formation ofcarbon-carbon sp³ bonds through the subplantation effect may only besignificant if sufficient ions are present in the particle stream.Preferably, at least 15% of the particles will comprise ions. In someembodiments, particularly at very low deposition pressures, thefilm-forming particle flux will comprise over 90% ions.

When depositing using a plasma beam source, the incident power providedto the coupling electrode will generally be between about 50 and 700watts, ideally being between about 200 and 300 watts. Where oppositesides of a substrate will be simultaneously coated, two plasma beamsources may be provided, preferably having independent radiofrequencygenerators which are phase-matched, ideally being synchronized in amaster/slave configuration. Radiofrequency reflected power willgenerally be between about 5 and 70 watts, and should be minimized byselection of proper network elements.

The magnetic containment field coil nearest the substrate may beprovided with a current of between 1 and 8 amps, ideally being about 7amps. The outer field coil will have between one-half and 5 amps ofcurrent flowing therethrough, wherein the current is the reversepolarity of the inner coil current. Gas flow rates of from 5 sccm to 30sccm are sufficient to maintain the plasma, with the gas flow rateideally being about 18 sccm. Igniting the plasma is facilitated byproviding an initial burst of between 40 and 50 sccm of N₂ gas. Anitrogen gas flow may be maintained for nitrogenation of the film.

The plasma beam source is capable of depositing ions with an energy ofbetween about 10 eV and 500 eV, while the optimal energy for depositionof carbon is generally between about 80 and 120 eV per carbon atom. Thehydrogen content may be between about 8 and 18 atomic percentage, whiledopant gases of between 0.7 atomic percent and 10 atomic percent,typical dopant gases including N₂, or PH₃. Carbon deposition rates ofbetween 2 and 12 Å per second can be provided by plasma beam sourcedeposition methods within the above operating ranges, ideally beingbetween about 8 and 9 Å per second to provide the highest quality films.Deposition times of between about 6 and 30 seconds are generally used atthese rates to provide a sufficient protective coating for magneticrecording media. In work in connection with the present invention, M.Weiler et al. describes the preparation and properties of highlytetrahedral hydrogenated amorphous carbon deposited using a plasma beamsource in the journal Physical Review B, vol. 53, pp. 1594-1608 (1996),the full disclosure of which is hereby incorporated by reference.

Although the plasma beam source deposition systems and methods describedwith reference to FIGS. 3A and 3D have several advantages, including theability to accurately control the ion deposition energy and flux, theseplasma beam sources do have some disadvantages. One primary disadvantageof plasma beam source deposition is that the capacitively coupled plasmadensity, and hence the deposition rate, is relatively low. In order toincrease the ion density, it would be beneficial to provide higherpressures within the plasma confinement volume, preferably maintainingthe plasma at a pressure of 30 mTorr or more. Unfortunately, theionization coefficient tends to drop off at these higher pressures,thereby limiting the total plasma density. Specifically, it willgenerally be advantageous to maintain low deposition pressures for atleast two reasons. First, the proportion of ions in the particle streamdecreases with increasing pressures. Basically, at higher operatingpressures, gas scattering will reduce and disperse the ion energy. Infact, deposition of highly tetrahedral amorphous carbon at pressures ofover 30 mTorr when using the exemplary system is problematic, as filmsdeposited at such pressures are formed primarily with low energyradicals. Second, as pressures increase, the particle flux increasinglyincludes varying particle masses (C₂, C₄, C₆, C₈ . . . ). As uniformmass particles are preferred, plasma beam deposition will preferablytake place with pressures below 1 mTorr, ideally at a pressure ofbetween about 0.1 and 0.5 MTorr. This, in turn, generally limits thedeposition rates which may be achieved by plasma beam sources andmethods which rely solely on capacitative coupling to maintain theplasma.

The hybrid beam source of the present invention maintains theadvantageous ion energy control of the plasma beam source, but provideshigher plasma densities and enhanced deposition rates without relying onincreases in pressure. Referring once again to FIGS. 2 and 2A, hybridsource 30 combines an inductive ionization system 32 with a capacitivecoupling system 36 (similar to that used in the plasma beam sourcesdescribed above) to provide a high density and low pressure plasma. Theinductive ionization system will again be explained in isolation, herewith referenced to FIGS. 4A and B.

Inductive ionization system 32 comprises an alternating power source 90capable of generating frequencies in roughly theradiofrequency-microwave range, preferably providing a potential with afrequency of about 27.12 MHz (or some multiple thereof). Once again, afrequency matching network 92 is provided, but the power is here coupledto the plasma using antenna 94 disposed around the plasma container 52.Advantageously, this minimizes any self-biasing of the plasma relativeto the antenna, and minimizes deposition of source materials onto thewalls of the container itself.

Plasma within an inductive discharge may be energized in a non-resonantor resonant inductive mode. Preferably, a small DC magnetic field issuperimposed on the plasma volume to provide enhanced ion energytransfer and plasma densification through a process which is generallydescribed as resonant ionization.

Antenna 94 may be described as a dielectric wall around the axis of theplasma container. Alternatively, antenna 94 may be modeled as a singleloop inductive coil disposed about the plasma. Regardless, the potentialof the plasma with respect to the container surface remains low, whilethe plasma density is quite high.

Typically, antenna 94 surrounds a cylindrical plasma container having alength between one third and three times its diameter, preferably beingof nearly equal length and diameter. The antenna consists of a metalcylinder with a longitudinal slit. The superimposed static magneticfield B is generally normal to the axis of the plasma cylinder, and isapplied by at least one magnetic coil 96 adjacent the plasma container.Resonant ionization potentials and magnetic field strengths are morefully described by Professor Oechsner in Plasma Physics, vol. 15, pp.835-844 (1974), the full disclosure of which is incorporated herein byreference.

The mechanism which will provide plasma densification will apparently beElectron Cyclotron Wave Resonance (ECWR), rather than the related butdifferent phenomenon of Electron Cyclotron Resonance (ECR). Both ofthese mechanisms can be understood with reference to the dispersion ofan electromagnetic wave propagating parallel to a magnetic field, andmore specifically, by analyzing the refraction index and the propagatingvelocity (here being phase velocity Vp) as a function of frequency andmagnetic field strength. We know that the refraction index and propationvelocity are related as follows:

$\frac{\omega^{2}}{c^{2}k^{2}} = {\frac{v_{p}^{2}}{c^{2}} = \frac{1}{n^{2}}}$where n is the refractive index, c is the speed of light, ω is thefrequency of the electromagnetic wave, and k is the magnitude of thepropagation vector for the electromagnetic wave. An ordinary wave can beexplained as a superposition of right- and left-handed circularlypolarized electromagnetic waves. In the case of a plasma, we should alsoconsider the different charges and masses of the electrons and ions.From the right- and left-hand polarized wave equations, we find aresonance effect is provided when ω is equal to the cyclotron frequencyω_(c). Under these conditions, the refraction index goes to infinity, sothat the propagation velocity is zero. This condition is referred to asECR. Unfortunately, the wavelengths associated with ECR are generallylarger than the desired sizes of our plasma containers, so thatpractical application of ECR for plasma densification would bedifficult.

Fortunately, ECWR provides an alternative densification mechanism when ωis less than ω_(c). Neglecting the motion of ions due to their muchhigher mass, the dispersion relation for the right-hand polarized waveis approximated by:

$n_{R}^{2} = {\frac{c^{2}k^{2}}{\omega^{2}} = {1 - \frac{\omega_{p}^{2}/\omega^{2}}{1 - \left( {\omega_{c}/\omega} \right)}}}$ω_(p) is the plasma frequency. Generally, wave propagation is possiblewhen the phase velocity (and therefore the refractive index) ispositive. Schematic plots of the refractive index of a cold plasma andthe phase velocity of a cold plasma (both as a function of frequency)are given in FIGS. 4C and 4D. Examination of these plots reveals thatboth are positive below ω_(c). In fact, the refractive index for adriving potential having a frequency of 13.56 MHz will reach valuesabove 100. This means that wavelengths within the plasma may be reducedby 1/100 or more. If the wavelength can be reduced to the dimensions ofthe plasma container, it is possible to create standing waves in theplasma which provide a resonant effect. This ECWR will depend on themagnetic filed strength as well as the plasma container dimensions. Ifour plasma container has a diameter a, this resonant effect cangenerally be achieved if:

$k_{r} = {\frac{2\pi}{\lambda} = {\frac{\pi}{a}\left( {{2\;\mu} + 1} \right)}}$μ=1, 2, 3, . . . , λ is the wavelength, and k_(r) being the resonantmagnetic field. The resonance can be tuned by varying the refractiveindex of the plasma. For ECWR, we will want to take into account thatthe refractive index for the right-hand polarized wave will depend onboth the magnetic field and the plasma frequency. The variation of n_(r)with the plasma frequency complicates this tuning somewhat, because theplasma frequency itself depends on the plasma density, which will, inturn, change with the degree of excitation of the plasma.

It is possibly to combine the densifying effects of inductive ionizationon low pressure plasmas with the capacitive coupling ion beam extractionof the plasma beam source to greatly enhance deposition rates.Unfortunately, inductive ionization does not generally produce a uniformplasma density. Hence, such a hybrid deposition system, without furthermodification, produces a non-uniform ion stream and deposition process.For these reasons, the present invention further provides a quasi-staticresonant ionization magnetic field, as will be explained with referenceto FIGS. 2 and 2A.

Referring once again to FIG. 2A, hybrid source 30 makes use of a plasmawhich is capacitively coupled so as to provide a stream of plasma ionsthrough extraction grid 64. To promote effective capacitive coupling,the plasma is maintained at a relatively low pressure, preferably below1 mTorr. To enhance the density of the plasma, an inductive powertransfer is locally achieved using antenna 94 of inductive couplingsystem 32. The DC plasma potentially from capacitative coupling, andhence the ion acceleration energy, is typically about 20 to 40 volts atall surfaces. Advantageously, ion energy can be selectively controlledby varying the DC bias of the extraction grid, as described above. Asimilar combination of inductive and capacitative coupling was describedfor sputter treatment of dielectric samples by Dieter Martin in a 1995dissertation for Universität Kaiserslavtern, Fachbereich Physik,Germany. That reference more fully explains the independent variation ofion energy and ion current density, similar to that applied in thehybrid deposition system of the present invention.

Ion/radical fluxes from hybrid source 30 may be enhanced using theinductive coupling system 32. To homogenize the ion stream produced byhybrid source 30, a slow moving resonant ionization magnetic field isapplied by quasi-static magnetic field generation system 34.

The preferred quasi-static magnetic field generation system makes use ofa plurality of coils 96 disposed radially about the plasma containmentvolume. Field rotator 100 selectively energizes coils 96 in opposedpairs, to apply a fairly uniform magnetic field throughout the plasma.The opposed coils are energized in the same direction, but only briefly,after which an alternate pair of transverse magnetic coils are energizedto apply a magnetic field B₂. Thereafter, the original coils may bereenergized, but with the opposite polarity so that magnetic field B₃,and then field B₄ are produced.

Field rotator 100 produces a magnetic field which effectively rotatesthrough the plasma containment volume with a rotational frequency whichis much less than the driving frequency of inductive coupling system 32,generally being less than 10,000 Hz, and often being less than 100 Hz.Thus, the rotating magnetic field provides resonant enhancement of theinductive coupling of a truly static resonant field. However, therotation of the magnetic field densifies a much broader region of theplasma, and thereby provides a much more homogeneous ion stream.Moreover, the moving magnetic field may also further density the plasmaby a churning effect, increasing the collisions between the energeticplasma particles to provide still further increases in deposition rateand energy transfer efficiency.

A typical hybrid source will have a container volume with an internalradius of about 5 cm, and a length between the coupling electrode andthe extraction grid of about 8½ cm. Such a hybrid source will require anionizing energy of between about 100 and 1000 watts, when driven at afrequency of about 13.56 MHz (or some multiple thereof). Clearly, a widevariety of alternative container geometries and sizes may be provided,within the scope of the present invention.

When using hybrid source 30 for deposition or etching, the plasmacontainer and deposition vessel surrounding the substrate are evacuated,preferably at a relatively high speed of about 2,000 liters per second.The ambient pressure during deposition will preferably be kept at about5×10⁻⁴ mbar. Once again, a short burst of N₂ gas is superimposed on asteady flow of the source gas to facilitate striking of the plasma, anda gas comprising nitrogen may be continuously supplied wherenitrogenation is desired. A burst on the order of a few millisecondswill suffice, or, alternatively, a high voltage pulse striker circuitmay be used with similar results. Ion current densities aresubstantially higher than the 0.1 to 0.7 mA/cm² provided by plasma beamsources, and may provide carbon deposition rates of between about 20 to100 Å per second.

Although hybrid source 30 is a preferred embodiment, a wide variety ofalternative systems may also be used. For example, the moving magneticfield may be provided by mechanically rotating one or more coils aboutthe plasma containment volume.

A still further alternative deposition system will be described withreference to FIG. 5. As illustrated, magnetic disk 2 is simultaneouslycoated on both sides by a pair of filtered cathodic arc sources 100.Each cathodic arc source includes a high density carbon target 102 whichis used as a cathode. Here, a plasma is maintained by an electricalpotential of the cathode relative to a graphite extractor anode 104 oncethe chamber has been evacuated through evacuation port 106.

Generally, cathodic arc deposition relies on a low voltage discharge atpressures of less than 10⁻⁵ mbar. Vaporized electrode material in theform of highly ionized intraelectrode plasma provides current transportbetween the cathode and anode. Typically, the solid cathode is consumedthrough microscopic localized regions of very high current density andtemperature, the cathode typically being an electrically conductivedeposition material such as a metal, carbon, or highly dopedsemiconductor. Advantageously, the kinetic energy of ions can beelectrostatically varied by biasing the substrate relative to thecathode. Energetic bombardment of the film using cathodic arc source 100can produce dense and continuous films through subplantation, asdescribed above. High deposition rates of between 30 and 100 Å persecond, together with high throwing power (the ability to coat uniformlyin three dimensions) are also provided by the intense ion flux. Toinitiate the arc, piezo system 108 passes through the wall of thedeposition chamber using a linear and rotary feedthrough 110 so as toinitially energize a graphite striker 112. Water cooling 114 helpsconfine the discharged energy to the deposition system.

Unfortunately, cathodic arc systems suffer from the expulsion ofmacroparticles (together with the plasma) from the surface of thecathode. The inclusion of these macroparticles can seriously limit thequality of films grown on substrates placed in front of the cathode.Therefore, source 100 blocks the direct path between the cathode and themagnetic recording media or other substrate to be coded using acurvilinear duct 116. Magnetic field coils 118 direct the desiredparticles through curvilinear duct 116, effectively filtering out themajority of the macroparticles. The use of baffles 120, and an irregularduct surface formed by bellows 122, helps to prevent the macroparticlesfrom bouncing along the curvilinear duct, thereby providing a moreeffective filter. The duct will typically be about 7.3 inches indiameter, while the curve may have a centerline radius of about teninches.

The filtered ion stream may be optionally accelerated towards thesubstrate using an acceleration grid 124. Alternatively, the substrateitself may be biased. To provide a more uniform deposition process, thefiltered ion stream may also be scanned over the substrate surface usinga raster magnetic field supplied by raster coils 126. Optionally, theion stream may be monitored through viewport 128. Steering magneticfields may also be provided at the cathode by steering coils 129.

It would be advantageous to minimize the macroparticles ejected from thecathode, rather than relying entirely on filtering. Toward that end, thepresent invention provides cathodes which are adapted to distribute anarc over a diffuse cathodic surface area, rather than forming a numberof discrete arc spots or jets. To provide such a distributed cathodicarc over an active region 130 of cathodic source 102, the power per unitarea is generally raised to a sufficient level for the active region toreach a critical temperature.

Cathodic arc deposition of graphite is particularly problematic, asgraphite in general is difficult to evaporate or sublime by electricalheating, largely because of its anomalous negative temperaturecoefficient of electrical resistivity (up to about 1,200° K). Graphiteis generally porous in nature, leading to large quantities ofmacroparticles being ejected during arcing. While the curvilinear ductfilter described above has proven effective at limiting the amount ofmacroparticles reaching the substrate, this structure also produces amagnetic pinching of the plasma stream, which reduces the area ofdeposition and tends to produce inhomogeneity in the thickness of thedeposited films. Additionally, over a long period of time, thecontamination of the filter duct walls can be disadvantageous, ascharged carbon dust from the wall may become entrapped in the plasmastream and contaminate the film.

To reduce macroparticle content from a graphite target, the temperatureof the cathode at or near the surface is increased to a temperatureabove the minimum point in the resistivity versus temperature curve forvarious types of graphite. Ideally, the temperature will be raisedsubstantially beyond this minimum resistivity temperature to enhanceohmic heating and thus evaporate the graphite more effectively. Toprovide a more stable process, it is generally advantageous to make useof a direct current cathodic arc, in which the arc itself can have aoverall lifetime of minutes, unlike spot or transient arcs which canappear and dissipate across the surface of the cathode within a timespan on the order of a few nanoseconds. The goal here is to enhance theeffect of local heat accumulation at the surface of the cathode, and topromote this heat trapping process on a time scale which issignificantly longer than that of known arc deposition systems. Work inconnection with the present invention has shown that continuous DC arcsmay be produced with durations of over 1 minute and preferably of over 3minutes.

Energy conservation at the cathode implies that the energy input andenergy output are equal. Energy is generally supplied to the cathodesurface through ohmic heating, ion bombardment, and Nottingham heating.Energy will be lost during the process through electron emissioncooling, evaporation cooling, and heat transfer by conduction,radiation, and convection.

The carbon cathode itself may optionally be prepared by compressing highpurity graphite powder at a hydrostatic pressure of between about 130and 150 MPa. The density of such a cathode will typically be betweenabout 1.5 and 1.7 g/cm³. To enhance the heat trapping at the cathodesurface, the cathode can be thermally insulated with thermal insulation132.

When the arc is first struck, the cathodic discharge evolves as avisible microscopic dot with a plasma ball, similar in appearance toknown cathode vacuum arcs. At the initial stage of arc triggering, thearc voltage is about 20 volts, which is typical of spot arcs for thesame arc current. Sometime after ignition, however, the single cathodicspot will evolve into a diffuse active area, preferably being at least 2cm². Ideally, the surface temperature within that area reaches a valuenearing the sublimation temperature of graphite, often being over 2,000°C. The steady state distributed arc mode may be characterized by a meanarc voltage value that fluctuates over about 25 volts, ideally beingbetween about 30 and 33 volts. The imposition of a steering magneticfield may decrease the transition time from the spot mode to thedistributed arc mode.

A reduction in macroparticle content may be visible observed as areduction of the number of incandescent particles within the plasma ascompared to the standard spot arc. A diffuse plasma cloud is formed overthe cathode surface, and the wide amplitude fluctuations characteristicof the spot arc are reduced. Additionally, the audible rattling noiseoften provided by filter cathodic arcs is replaced by a notably quietererosion process. Erosions of 2 mg/s have been measured over a series ofruns accumulating a total of 5 minutes of arcing.

Rise in the cathodic temperature may conveniently be produced by thereverse ion bombardment and Joule heating of cathode 102. Thermalinsulation 132 may also prevent dissipation of the heat energy tocooling water system 114. Thermal insulation may be disposed over aselected portion of cathode 102 so as to selectively control the sizeand position of active region 130.

The distributed cathodic arc of the present invention produces asignificantly lower total current density and a higher spatialuniformity in ion current density. Such a distributed arc may make useof a higher arc voltage than in the more conventional cold cathodic arcsources, as well as a reduced amplitude in arc current oscillations,which will help to decrease the macroparticle content of the associatedplasma. Reduction of macroparticles will reduce cleaning and maintenanceof a filter duct, and may even allow unfiltered deposition. Unfilteredcarbon distributed arc films may be produced having densities of over 3g/cm³ with a mean ion energy of 18 eV, at over 50 Å/s, by a particleflux with an ionization of over about 60%.

EXPERIMENTAL

Films were deposited on aluminum substrates over a magnetic layer usingopposed plasma beam sources and acetylene plasmas. The depositionconditions are summarized in Table 1. These conditions gave a highlyionized plasma and an ion beam energy of about 120 eV/C ion within awell-defined energy window.

TABLE I Item A-side B-side Condition rf-input power 250 W 250 WPhase-matched rf-reflected 5 ± 1 W 7 ± 1 W Stable during depositionpower Inner Coil 7.0 Å 7.0 Å Current Outer Coil −0.5 Å −0.5 Å ReversePolarity Current Gas-flow rate 18 sccm 18 sccm Plasma ignited at 43 sccmwith a burst of N₂ gas Dep-Rate 8-9 Å/s 8-9 Å/s Deposition time variedfrom 10-30 s

The acetylene gas flow rate was pre-set (by an electronic controller) topromote diamond-like bonding in the ta-C:H carbon films, rather thanoptimizing the deposition rate. Gas flow rates are in standard cubiccentimeters per second (sccm). The matching-network circuit passiveelements were pre-tuned so as to minimize the ratio of P_(ref)/P_(in)(power reflected over power input) at the above-mentioned acetylene flowrate.

The rate phase state was triggered using a short burst of N₂ gas(lasting less than 0.1 s) superimposed on the steady flow of C₂H₂. Thepressure of the chamber during deposition was in the region of 5*10⁻⁴mbar. Textured and untextured smooth disks were coated, and the carboncoatings were characterized using ellipsometry, electron energy lossspectroscopy (EELS) and Raman finger-printing. The textured disks werelubed using conventional lube processes, and underwent abrasive tapetests as well as accelerated start-stop tests.

Table II summarizes the variation of physical properties of the films asa function of thickness. The average ion energy per carbon ion wasuniformly maintained at about 100 eV. The spatial homogeneity of thefilms is gauged in both the radial as well as angular positions.Generally, G-peak and D-peak are V-peak positions in Raman spectroscopy,while the associated Δ values describe peak widths. Selket voltage isthe output voltage of a light sensor for abrasive wear test equipmentmanufactured by Selket Co. The higher the output voltage, the moreserious the wear.

TABLE II thickness Selket Voltage G-peak ± G-peak Δ ± RMS * R_(a) RamanPlasmon Item (A) ± 10 (mV) 5 cm⁻¹ 5 cm⁻¹ (Angs) I_(d)/I_(g) Peak (eV)Cell 1 40 3 1494 150 3 0.24 31.4 Cell 2 50 2 1498 152 4 0.48 30.0 Cell 370 5 1508 138 6 0.5 29.5 Cell 4 80 7 1507 137 6 0.6 29.8 Cell 5 100 61509 130 9 0.7 29.7 Cell 6 200 7 1509 130 8 1.0 25.5

One noteworthy observation from the Raman spectra is the increase inboth the position of the G-peak as well as the I_(d)/I_(g) ratio (thearea ratio of the D and G peaks) with increasing film thickness. Thisshows that the percentage of C-C sp³ content in the bulk of the filmsincreases with decreasing thickness. D-peak bandwidth also increaseswith decreasing film thickness within the range monitored. The bandwidthof the D-peak in the optimized films is above 150 cm⁻¹, indicating verylow levels (or absence) of graphitic phase clustering within thediamond-like carbon amorphous matrix. This result is consistent with therelatively high Plasmon-peak measured from theelectron-energy-loss-spectroscopy (EELS). Plasmon peak is the energy ofa type of excitation called a plasmon. It is a quantum of chargedparticle cloud vibration. The energy value is directly related to thecharged particle (e.g., electron) density.

The Plasmon-peak E_(p) is representative of the density of the films.Thus, taking the E_(p) of diamond to be 34 eV, it is estimated that themost-diamond-like ta-C:H films have above 80% C-C sp³ bonding (this isindependent of whether there is long range order or not).

Discs were coated with ta-C:H films under a wide variety of rf-power andgas-feedstock flow rates. These films were then tested for frictionbuild-up and wear durability using a conventional accelerated contactstart/stop (CSS) test. Prior to testing, the disks were lubed and lubethickness was found to vary between 16-23 Å, corresponding to a carbonfilm thickness range of 30 Å to 150 Å. Each test consisted of 500cycles, and the disks were tested on both sides at 300 rpm. The averagedcoefficients of friction (μ_(s)) are plotted against thickness of thefilms in Table III. The variation of μ_(s) is found to be between 0.5 to1.5, corresponding to a thickness range from 40 Å to 150 Å. Of the 16disks that underwent the accelerated CCS test, all but one passed.

TABLE III rf power Gas flow- Deposition Coefficient of static (Watts)rate (sccm) time(s) friction μ_(s) 500 20 10 1.6 100 12 30 1.8 500 20 61.5 100 20 6 1.6 300 16 6 1.4 500 20 6 1.5 500 20 30 2.0 500 20 12 1.5500 20 6 1.9 100 12 6 1.7 100 12 6 1.6 100 12 30 1.6 100 16 18 1.5 30016 6 1.3

Disks were also coated with highly tetrahedral amorphous carbon using afiltered cathodic arc. Initially, two disks were coated with a staticion stream, producing coatings which varied considerably from the centerto the edge. Estimating coating thicknesses using interference colors,and assuming an index of refraction of 2.5, coating thicknesses variedat least between 1,250 Å and 500 Å.

Raw data from Selket abrader tests are provided in FIGS. 6A and B. Overthe two 120 second tests, no debris was seen on the tape. Only a veryfaint wear track was found after tests were complete.

Peak friction of the disks was also measured as a function of the numberof start/stop cycles. The results of these tests are provided in FIG. 7.

The Raman spectra of the filtered cathodic arc disks were also measured,and the results are provided in FIG. 8. Generally, these resultsindicate that a film can be deposited using a cathodic arc source whichincludes a G-peak in the area of about 1518, and having a G width ofapproximately 175. The pseudo band gap of this film appears to beroughly 1.68 eV, while the refractive index is approximately 2.5. Thecomplex portion of the optical index of refraction, K, appears to beapproximately 0.08 for the film.

An additional disk was coated, this time on both sides, using a filteredcathodic arc source. The ion stream was swept over the surface of thesubstrate by manipulating permanent magnets placed on either side of thechamber. No bias was applied to the scanned substrate. Although thescanning mechanism here was quite simple, a more uniform depositionlayer was provided.

Although the foregoing invention has been described in some detail, byway of illustration and example, for purposes of clarity ofunderstanding, it will be obvious that certain changes and modificationsmay be practiced within the scope of the appended claims.

1. A method for formation of an ion beam that provides carbon depositionover a substrate, the ion beam produced by inductively ionizing anacetylene plasma within a plasma volume and capacitatively coupling theplasma so as to form a stream of ions from within the plasma volume, themethod comprising: moving a magnetic field through the plasma volume topromote even resonant inductive ionization and homogenize the ion beamwhich deposits carbon over the substrate, wherein the magnetic fieldrotates with a frequency of less than 10,000 Hz.
 2. A method as claimedin claim 1, wherein moving the magnetic field comprises selectivelyenergizing magnetic coils disposed about the plasma volume.
 3. A methodas claimed in claim 1, wherein the magnetic field rotates through theplasma volume with a frequency which is much less than the frequency ofan alternating induction potential within the plasma volume.
 4. A methodas claimed in claim 1, wherein the magnetic field is transverse androtates about an axis which is substantially normal to a capacitativelycoupled extraction grid within the plasma volume.
 5. A method as claimedin claim 1, wherein the magnetic field rotates with a frequency of lessthan 100 Hz.
 6. A method as in claim 1, wherein the carbon is depositedon the substrate at a rate in a range from 20 Å per second to 100 Å persecond.
 7. A method as in claim 1, wherein the substrate includes amagnetic recording medium.
 8. A method as in claim 1, wherein thesubstrate includes a semiconductor material.